In providing a combination of process steps which yield valuable products from natural gas heretofore considered valueless, the invention utilizes known technology for (1) generating a synthesis gas of carbon monoxide and hydrogen from reaction of methane and water; (2) generating carbon dioxide and hydrogen by the water gas shift reaction of carbon monoxide with water; (3) synthesis of methanol or liquid hydrocarbons by reaction of carbon monoxide and hydrogen; and (4) tertiary recovery of petroleum by injection to a spent underground reservoir of carbon dioxide which contains little methane, it being known that methane reduces solubility of carbon dioxide in petroleum.
The natural gases of interest in the process of this invention have been heretofore regarded as having no significant commercial value. Natural gas containing mixtures of carbon dioxide and methane in about equal volumes and those still richer in methane have been processed to separate methane from carbon dioxide and thus provide fuel gas of pipe line quality. However, it has been considered uneconomic to produce natural gas from extensive known reservoirs in which the gas contains 75% by volume, more or less, of carbon dioxide. The cost for separation of the methane content is too great in comparison with value of the recovered methane to support construction and operation of separation facilities. Assuming a use for the carbon dioxide in tertiary recovery at petroleum reserviors within a distance which can justify piping the gas, these mixtures are unsuitable because of their content of methane which is known to inhibit solubility of carbon dioxide in petroleum.
For a great number of years, natural gas had been considered to be the proper natural source material for generation of synthesis gas containing carbon monoxide and hydrogen to be used in synthesis of methanol, for synthesis of hydrocarbons by the well-known Fischer-Tropsch reaction, or the like. As the cost of natural gas has risen, more attention is being given to the vast deposits of coal in the United States and elsewhere as a source of synthesis gas.